The future of packaging goals will be met by increasing the number of input/output (I/O) leads and the density of chips, while simultaneously reducing the number of internal connections and overall package size. Today's packaging with fewer interconnection links, decreases potential failure points, reduces circuit resistance and can shorten the circuit length, thereby enabling devices to operate at higher speeds. The need to create faster and more reliable integrated circuits, while reducing integrated circuit (IC) packaging size, is driven by consumer demand for these products in end-user applications, such as, cellphones, camcorders, portable music players, computers and televisions.
Flip chip packaging is an advanced IC packaging design that meets the demand for faster IC technology with more I/O leads. Flip chip packaging is a technique of mounting the active side of a chip toward the substrate (i.e.—upside down placement of the bumped die relative to wire-bonding techniques). This packaging technique is currently the design with the shortest path from the chip to the substrate, thereby providing a good electrical connection for high speed signals.
A common problem with flip chip technology is that the resin employed to reduce stresses arising from the excessive coefficient of thermal expansion (CTE) mismatch between the chip and the substrate is subject to bleed out or resin fillet formation. This resin bleed phenomena forms a fillet that spills out onto the bond finger region, thereby forcing the wire bond connection to the bond finger region to be laterally displaced so as to ensure a good electrical connection. This lateral displacement of the wire bond connection to the bond finger region causes an increase in package size.
The typical size of the resin fillet is about 1.5-3 mm, resulting in a lateral package size increase of 3-6 mm due to the resin fillet on both sides of the die. For a nominal package size of 12×12 mm, this would result in a package size increase of 25-50% and an increase in the package footprint (area) of 50-100% over what it would be if it were possible to connect within the resin fillet.
Thus, a need still remains for eliminating resin fillet formation and the corresponding increase in package size. In view of the semiconductor industry's demands, it is increasingly critical that answers be found to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.